A helmet is a form of protective gear worn to protect the head from injuries. More specifically, a helmet aids the skull in protecting the human brain. Ceremonial or symbolic helmets (e.g. UK policeman's helmet) without protective function are sometimes used, the oldest known use of helmets was by Assyrian soldiers in 900 BC, who wore thick leather or bronze helmets to protect the head from blunt object and sword blows and arrow strikes in combat. Soldiers wear helmets, often made from lightweight plastic materials.

The word helmet is diminutive from helm, a medieval word for protective combat headgear. The medieval great helm covers the whole head and often is accompanied with camail protecting throat and neck as well. Originally a helmet was a helm which covered the head only partly.

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Helmets attempt to protect the user's head by absorbing mechanical energy and protecting against penetration, their structure and protective capacity are altered in high-energy impacts. Beside their energy-absorption capability, their volume and weight are also important issues, since higher volume and weight increase the injury risk for the user's head and neck. Anatomical helmets adapted to the inner head structure were invented by neurosurgeons at the end of the 20th century.

Helmets used for different purposes have different designs, for example, a bicycle helmet must protect against blunt impact forces from the wearer's head striking the road. A helmet designed for rock climbing must protect against heavy impact, and against objects such as small rocks and climbing equipment falling from above. Practical concerns also dictate helmet design: a bicycling helmet should be aerodynamic in shape and well ventilated, while a rock climbing helmet must be lightweight and small so that it does not interfere with climbing.

Baseball batting helmets have an expanded protection over the ear, which protects the jaw from injury.

Motorcycle helmets often have flip-down face screens for rain and wind protection, and they may also have projecting visors to protect the eyes from glare.

Hard hats for construction workers are worn mainly to protect the wearer from falling objects such as tools.

Helmets for riot police often have flip-down clear visors and thick padding to protect the back of the neck.

Modern firefighter's helmets protect the face and back of the head against impact, fires and electricity, and can include masks, communication systems, and other accessories.

Welding helmets protect the eyes and face and neck from flash burn, ultraviolet light, sparks and heat. They have a small window, called a lens shade, through which the welder looks at the weld; for arc welding this window must be much darker than in blowtorch goggles and sunglasses.

Mixed martial arts helmets have ear pads to prevent serious injuries to the athletes, who do not usually endure such force to the ears.

Some watersports helmets, such as for underwater hockey or water polo, have ear-cages fitted which are designed to help prevent burst eardrums caused by an excessive water pressure resulting from a contact or percussion from other equipment involved in the sport.

Crash helmets for F1 racing drivers, their design and construction have evolved enormously. Nevertheless, head and neck trauma remains the greatest single injury risk to drivers.

Amelia Earhart wearing a helmet just before her transatlantic crossing of 1928

Historically, helmets have been made from a wide range of materials, including various metals, plastics, leather, and even some fibrous materials such as Kevlar. Ancient and medieval helmets were usually made of metals, often bronze, iron or steel, though some boar's tusk helmets were known to ancient Mycenae.

Some British gamekeepers during the 18th and 19th centuries wore helmets made of straw bound together with cut bramble.[1] Developed in the mid-19th century, the pith helmet, made of pith or cork, was often worn by Europeans in the tropics.

Military applications in the 19th-20th centuries saw a number of leather helmets, particularly among aviators and tank crews in the early 20th century; in the early days of the automobile, some motorists also adopted this style of headgear, and early football helmets were also made of leather. In World War II, American, Soviet, German, Italian and French flight crews wore leather helmets, the German pilots disguising theirs under a beret before disposing of both and switching to cloth caps.[when?] The era of the First and Second World Wars also saw a resurgence of metal military helmets, most notably the Brodie helmet and the Stahlhelm.

Modern helmets have a much wider range of applications, including helmets adapted to the specific needs of many athletic pursuits and work environments, and these very often incorporate plastics and other synthetic materials for their light weight and shock absorption capabilities, some types of synthetic fibers used to make helmets in the 21st century include Aramid, Kevlar and Twaron.[2]

In the 19th century, more materials were incorporated, namely leather, felt and pith, the pith helmet and the leather pickelhaube were important 19th century developments. The greatest expansion in the variety of forms and composition of helmets, however, took place in the 20th century, with the development of highly specialized helmets for a multitude of athletic and professional applications, as well as the advent of modern plastics, during World War I, the French army developed the Adrian helmet, the British developed the Brodie helmet, and the Germans produced the Stahlhelm.

Helmets since the mid-20th century have often incorporated lightweight plastics and other synthetic materials, and their use has become highly specialized, some important recent developments include the French SPECTRA helmet, Spanish MARTE helmet or the American PASGT (commonly called "Kevlar" by U.S. troops) and Advanced Combat Helmet, or ACH.

As the coat of arms was originally designed to distinguish noble combatants on the battlefield or in a tournament, even while covered in armour, it is not surprising that heraldic elements constantly incorporated the shield and the helmet, these often being the most visible parts of a knight's military equipment.

The common practice was to display a helmet as part of the coat of arms, above the shield, a practice maintained long after helmets themselves ceased to be used; in German heraldry, the helmet was even considered to be inseparable from the shield, in contrast to English heraldry, where the practice of displaying the helmet and crest alone with no shield whatsoever came into vogue in Victorian times. In most post-medieval heraldic traditions, the style, colour and position of the helmet became emblematic of the rank of the bearer. Rank was also often denoted by a coronet, usually either surmounting the shield or placed upon the helmet.

The practice of indicating peerage through the display of barred or grilled helmets first appeared around 1587-1615,[3] and the heraldic convention of displaying helmets of rank in the United Kingdom, which came into vogue around Stuart times, is as follows:[4]

1.
Bicycle helmet
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A bicycle helmet is designed to attenuate impacts to the head of a cyclist in falls while minimizing side effects such as interference with peripheral vision. The dominant form of helmet up to the 1970s was the leather hairnet style and this offered acceptable protection from scrapes and cuts, but only minimal impact protection, and was mainly used by racing cyclists. More widespread use of helmets began in the U. S. in the 1970s, after many decades, when bicycles were regarded only as childrens toys, many American adults took up cycling during and after the bike boom of the 1970s. Two of the first modern bicycle helmets were made by MSR, a manufacturer of mountaineering equipment, and Bell Sports and these helmets were a spin-off from the development of expanded polystyrene foam liners for motorcycling and motorsport helmets, and had hard polycarbonate plastic shells. The bicycle helmet arm of Bell was split off in 1991 as Bell Sports Inc. having completely overtaken the motorcycle, the first commercially successful purpose-designed bicycle helmet was the Bell Biker, a polystyrene-lined hard shell released in 1975. At the time there was no standard, the only applicable one, from Snell. Over time the design was refined and by 1983 Bell were making the V1-Pro, in 1984 Bell produced the Lil Bell Shell, a no-shell childrens helmet. These early helmets had little ventilation, in 1985, Snell B85 was introduced, the first widely adopted standard for bicycle helmets, this has subsequently been refined into B90 and B95. At this time helmets were almost all either hard-shell or no-shell, ventilation was still minimal due mainly to technical limitations of the foams and shells in use. Around 1990 a new technique was invented, in-mould microshell. A very thin shell was incorporated during the moulding process and this rapidly became the dominant technology, allowing for larger vents and more complex shapes than hard shells. The late 1990s and early 2000s saw advances in retention and fitting systems, with cradles which adjust precisely to the riders head and this resulted in the back of the head being less covered by the helmet, although more recent designs have largely addressed this. Since more advanced helmets began being used in the Tour de France, carbon fiber inserts are often used to increase strength, the Giro Atmos and Ionos, as well as the Bell Alchera were among the first to use carbon fiber. Some modern road and track racing bicycle helmets have a long tapering back end for streamlining and this type of helmet is mainly dedicated to time trial racing as they lack significant ventilation, making them uncomfortable for long races. Snells standard includes testing of random samples, in 1990 the Consumers Association market survey showed that around 90 % of helmets on sale were Snell B90 certified. By their 1998 survey the number of Snell certified helmets was around zero, there are two main types of helmet, hard shell and soft/micro shell. The American National Standards Institute created a standard called ANSI Z80.4 in 1984, later, the United States Consumer Product Safety Commission created its own mandatory standard for all bicycle helmets sold in the United States, which took effect in March 1999. In the European Union the currently applicable standards are EN1078,1997, in Australia and New Zealand, the current legally-required standard is AS/NZS2063

2.
Personal protective equipment
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Personal protective equipment refers to protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearers body from injury or infection. The hazards addressed by protective equipment include physical, electrical, heat, chemicals, biohazards, Protective equipment may be worn for job-related occupational safety and health purposes, as well as for sports and other recreational activities. Protective clothing is applied to categories of clothing, and protective gear applies to items such as pads, guards, shields, or masks. PPE is needed there are hazards present. PPE has the limitation that it does not eliminate the hazard at source. Any item of PPE imposes a barrier between the wearer/user and the working environment and this can create additional strains on the wearer, impair their ability to carry out their work and create significant levels of discomfort. Any of these can discourage wearers from using PPE correctly, therefore placing them at risk of injury, ill-health or, under extreme circumstances, death. Good ergonomic design can help to minimise these barriers and can help to ensure safe. Practices of occupational safety and health can use hazard controls and interventions to mitigate workplace hazards, the hierarchy of hazard controls provides a policy framework which ranks the types of hazard controls in terms of absolute risk reduction. At the top of the hierarchy are elimination and substitution, which remove the hazard entirely or replace the hazard with a safer alternative. If elimination or substitution measures cannot apply, engineering controls and administrative controls, Personal protective equipment ranks last on the hierarchy of controls, as the workers are regularly exposed to the hazard, with a barrier of protection. The hierarchy of controls is important in acknowledging that, while personal protective equipment has tremendous utility, Personal protective equipment can be categorized by the area of the body protected, by the types of hazard, and by the type of garment or accessory. The protective attributes of each piece of equipment must be compared with the expected to be found in the workplace. More breathable types of protective equipment may not lead to more contamination. Respirators serve to protect the user from breathing in contaminants in the air, there are two main types of respirators. One type functions by filtering out chemicals and gases, or airborne particles, the filtration may be either passive or active. Gas masks and particulate respirators are examples of type of respirator. A second type protects users by providing clean, respirable air from another source and this type includes airline respirators and self-contained breathing apparatus

3.
Human head
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In human anatomy, the head is the upper portion of the human body. It supports the face and is maintained by the skull, which encloses the brain. The human head consists of an outer portion surrounding the bony skull. The head rests on the neck, and is provided bony support for movement by the seven cervical vertebrae, the face is the anterior part of the head, containing the sensory organs the eyes, nose and mouth. The cheeks, on side of the mouth, provide a fleshy border to the oral cavity. To either side of the sit the ears. The twelve pairs of cranial nerves provide the majority of control to the head. The sensation to the face is provided by the branches of the trigeminal nerve, the sensation to other portions of the head is provided by the cervical nerves. The head receives blood supply through the internal and external carotid arteries and these supply the area outside of the skull and inside of the skull. The area inside the skull also receives blood supply from the vertebral arteries, the head contains sensory organs, two eyes, two ears, a nose and inside the mouth a tongue. The human head typically weighs between 5 and 11 pounds, human faces are easily differentiable to us due to our brains predispositions toward discriminating human facial forms. When observing a relatively unfamiliar species, all faces seem nearly identical, ancient Greeks had a method for evaluating sexual attractiveness based on the Golden Ratio, part of which included measurements of the head. In many cultures, covering the head is seen as a sign of respect, often, some or all of the head must be covered and veiled when entering holy places, or places of prayer. For many centuries, women in Europe, the Middle East and this trend has changed drastically in Europe in the 20th century, although is still observed in other parts of the world. People may cover the head for other reasons, a hat is a piece of clothing covering just the top of the head. This may be part of a uniform, such as a uniform, a protective device such as a hard hat. Different headpieces can also signify status, origin, religious/spiritual beliefs, social grouping, team affiliation, occupation, while numerous charts detailing head sizes in infants and children exist, most do not measure average head circumference past the age of 21. Reference charts for adult head circumference also generally feature homogeneous samples, one study in the United States estimated the average human head circumference to be 55 centimetres in females and 57 centimetres in males

4.
Brain
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The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. The brain is located in the head, usually close to the organs for senses such as vision. The brain is the most complex organ in a vertebrates body, in a human, the cerebral cortex contains approximately 15–33 billion neurons, each connected by synapses to several thousand other neurons. Physiologically, the function of the brain is to exert centralized control over the other organs of the body, the brain acts on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment, the operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. This article compares the properties of brains across the range of animal species. It deals with the human brain insofar as it shares the properties of other brains, the ways in which the human brain differs from other brains are covered in the human brain article. Several topics that might be covered here are instead covered there because more can be said about them in a human context. The most important is brain disease and the effects of brain damage, the shape and size of the brain varies greatly between species, and identifying common features is often difficult. Nevertheless, there are a number of principles of architecture that apply across a wide range of species. Some aspects of structure are common to almost the entire range of animal species, others distinguish advanced brains from more primitive ones. The simplest way to gain information about brain anatomy is by visual inspection, Brain tissue in its natural state is too soft to work with, but it can be hardened by immersion in alcohol or other fixatives, and then sliced apart for examination of the interior. Visually, the interior of the consists of areas of so-called grey matter, with a dark color, separated by areas of white matter. Further information can be gained by staining slices of tissue with a variety of chemicals that bring out areas where specific types of molecules are present in high concentrations. It is also possible to examine the microstructure of brain tissue using a microscope, the brains of all species are composed primarily of two broad classes of cells, neurons and glial cells. Glial cells come in types, and perform a number of critical functions, including structural support, metabolic support, insulation. Neurons, however, are considered the most important cells in the brain. The property that makes neurons unique is their ability to send signals to target cells over long distances

5.
Custodian helmet
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The custodian helmet is the modern name applied to the helmet worn by male police officers in England and Wales and certain other places around the world. It is synonymous with the bobby on the beat image, the custodian helmet is the headgear traditionally worn by male police constables and sergeants while on foot patrol in England and Wales. Officers of all ranks in most forces are issued a flat. Ranks above sergeant wear the cap only. It was first adopted by the London Metropolitan Police in 1863 to replace the top hat worn since 1829. The early Metropolitan Police helmet had a garter style badge on the front of the helmet which had the personal number and divisional letter in the centre. This was surrounded by a design which had the words Metropolitan Police around the outside and was topped with the reigning monarchs crown. This style changed in 1875, when a version of the brunswick star was adopted without the upturned brim seen in the previous style. There was much variety in the style of helmets during this period, the form of the helmets gradually converged with the foreign service and home service helmets adopted by the British army in the late-1870s. Some forces adopted the helmet without any badge, others designed their own, one force adopted an Australian style bush hat and one wore a helmet constructed of straw. The Home Office Pattern consisted of a helmet with the Brunswick star badge which would feature the reigning monarchs cipher, the top of the helmet had a rose top, which was a raised metal rose, largely used as an ornament to cover the ventilation hole. However, this process was largely unsuccessful, with many different designs being worn by todays police forces nationally. Internally, helmets up until the 1970s, and in areas the 1980s, had only a sweat band to allow it to sit correctly on the wearers head. Other helmet furniture included a top and in some cases a spike top. During the 1970s and 1980s, before specially adapted riot helmets were produced, officers were expected to conduct public order, the cork construction provided little protection against attack and hand-thrown missiles. In order to more protection, the construction of the helmets changed. Visually they remained the same, however instead of being constructed of cork they were now out of a very hard wearing plastic material. Internally, they were padded with foam which was fitted into the shell of the helmet with a webbing-style harness to allow it to sit on the head in the correct manner

6.
Military history of the Neo-Assyrian Empire
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The Neo-Assyrian Empire arises in the 10th century BC. Ashurnasirpal II is credited for utilizing sound strategy in his wars of conquest, while aiming to secure defensible frontiers, he would launch raids further inland against his opponents as a means of securing economic benefit, as he did when campaigning in the Levant. The result meant that the prosperity of the region would fuel the Assyrian war machine. Ashurnasirpal II was succeeded by Shalmaneser III, although he campaigned for 31 years of his 35-year reign, he failed to achieve or equal the conquests of his predecessor, and his death led to another period of weakness in Assyrian rule. As such, costly battles raged taking tolls on Assyrian manpower, Esarhaddon succeeded in taking lower Egypt and his successor, Ashurbanipal, took the southern upper half of Egypt. However, by the end of the Ashurbanipals reign it appears that the Assyrian Empire was falling into another period of weakness and it appears that years of costly battles followed by constant rebellions meant that it was a matter of time before Assyria ran out of troops. The loss of the outer regions meant that troops were gone too. By 605 BC, independent political Assyrian records vanish from history, Mesopotamia was the site of some of the earliest recorded battles in history. In fact, the first recorded battle was between the forces of Lagash and Umma c.2450 BC, like many Mesopotamian records, it contains elements of fiction. The ruler of Lagash, Eanatum, was inspired by the god Ningirsu to attack the kingdom of Umma. Eanatum, although having triumphed, was struck in the eye by an arrow, after the battle, he proudly documented the behavior of the vultures. The Assyrian empire has at times described as the first military power in history. The earliest Old Assyrian king Tudiya was a contemporary of Ibrium of Ebla and it evolved from the Akkadian Empire of the late 3rd millennium BC. Assyria was a nation under the rule of Ilushuma, who founded colonies in Asia Minor and raided Isin. According to legend, Sargon, the first king of the Akkadian Kingdom, was discovered by a gardener in Mesopotamia in a basket. In time, he would found the city of Agade and raise an army of 5,400 men and his inscriptions boast of 34 victories and 5,400 men eating bread before Sargon, exemplifying both the vast manpower and the obedience of his troops. Though small by the standards of later kings, Sargons army was larger and more sophisticated than others of the time, utilizing a combination of spears and missile weapons. Bronze swords and four wheeled chariots brushed aside any resistance as he carved out his empire, which may well have included parts of the Mediterranean, Anatolia and western Iran

7.
Sword
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A sword is a long bladed weapon intended for slashing or thrusting. The precise definition of the term varies with the epoch or the geographical region under consideration. A sword consists of a blade attached to a hilt. The blade can be straight or curved, thrusting swords have a pointed tip on the blade, and tend to be straighter, slashing swords have sharpened cutting edge on one or both sides of the blade, and are more likely to be curved. Many swords are designed for thrusting and slashing. Historically, the sword developed in the Bronze Age, evolving from the dagger, the later Iron Age sword remained fairly short and without a crossguard. The word sword continues the Old English, sweord, the use of a sword is known as swordsmanship or as fencing. In the Early Modern period, western sword design diverged into two forms, the thrusting swords and the sabers. The thrusting swords such as the rapier and eventually the smallsword were designed to impale their targets quickly and their long and straight yet light and well balanced design made them highly maneuverable and deadly in a duel but fairly ineffective when used in a slashing or chopping motion. A well aimed lunge and thrust could end a fight in seconds with just the swords point, the saber and similar blades such as the cutlass were built more heavily and were more typically used in warfare. Built for slashing and chopping at multiple enemies, often from horseback, most sabers also had sharp points and double edged blades, making them capable of piercing soldier after soldier in a cavalry charge. Sabers continued to see use until the early 20th century. The US Navy kept tens of thousands of sturdy cutlasses in their armory well into World War II, non-European weapons called sword include single-edged weapons such as the Middle Eastern scimitar, the Chinese dao and the related Japanese katana. The Chinese jian is an example of a non-European double-edged sword, the first weapons that can be described as swords date to around 3300 BC. They have been found in Arslantepe, Turkey, are made from arsenical bronze, some of them are inlaid with silver. The sword developed from the dagger when the construction of longer blades became possible, from the late 3rd millennium BC in the Middle East, first in arsenic copper, then in tin-bronze. Blades longer than 60 cm were rare and not practical until the late Bronze Age because the strength of bronze is relatively low. These are the type A swords of the Aegean Bronze Age, one of the most important, and longest-lasting, types swords of the European Bronze Age was the Naue II type, also known as Griffzungenschwert

8.
Arrow
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An arrow is a shafted projectile that is shot with a bow. It predates recorded history and is common to most cultures, an arrow usually consists of a shaft with an arrowhead attached to the front end, with fletchings and a nock at the other. The oldest evidence of stone-tipped projectiles, which may or may not have been propelled by a bow, dating to c.64,000 years ago, were found in Sibudu Cave, South Africa. The oldest evidence of the use of bows to shoot arrows dates to about 10,000 years ago and they had shallow grooves on the base, indicating that they were shot from a bow. The oldest bow so far recovered is about 8,000 years old, archery seems to have arrived in the Americas with the Arctic small tool tradition, about 4,500 years ago. Arrow sizes vary greatly across cultures, ranging from eighteen inches to five feet, however, most modern arrows are 75 centimetres to 96 centimetres, most war arrows from an English ship sunk in 1545 were 76 centimetres. Very short arrows have been used, shot through a guide attached either to the bow or to the archers wrist and these may fly farther than heavier arrows, and an enemy without suitable equipment may find himself unable to return them. The shaft is the structural element of the arrow, to which the other components are attached. Traditional arrow shafts are made from wood, bamboo or reeds, while modern shafts may be made from aluminium, carbon fibre reinforced plastic. Such shafts are made from an aluminium core wrapped with a carbon fibre outer. The stiffness of the shaft is known as its spine, referring to how little the shaft bends when compressed, hence, an arrow which bends less is said to have more spine. In order to strike consistently, a group of arrows must be similarly spined, center-shot bows, in which the arrow passes through the central vertical axis of the bow riser, may obtain consistent results from arrows with a wide range of spines. Higher draw-weight bows will generally require stiffer arrows, with more spine to give the amount of flex when shot. The weight of a shaft can be expressed in GPI. The length of a shaft in inches multiplied by its GPI rating gives the weight of the shaft in grains, for example, a shaft that is 30 inches long and has a GPI of 9.5 weighs 285 grains, or about 18 grams. This does not include the elements of a finished arrow. Sometimes a shaft will be made of two different types of wood fastened together, resulting in what is known as a footed arrow, known by some as the finest of wood arrows, footed arrows were used both by early Europeans and Native Americans. Footed arrows will typically consist of a length of hardwood near the head of the arrow

9.
Kevlar
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Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed by Stephanie Kwolek at DuPont in 1965, this material was first commercially used in the early 1970s as a replacement for steel in racing tires. Typically it is spun into ropes or fabric sheets that can be used as such or as an ingredient in composite material components and it is also used to make modern drumheads that withstand high impact. When used as a material, it is suitable for mooring lines. A similar fiber called Twaron with roughly the same structure was developed by Akzo in the 1970s, commercial production started in 1986. Poly-paraphenylene terephthalamide – branded Kevlar – was invented by Polish-American chemist Stephanie Kwolek while working for DuPont, in 1964, her group began searching for a new lightweight strong fiber to use for light but strong tires. The polymers she had been working with at the time, poly-p-phenylene-terephthalate and polybenzamide, formed liquid crystal while in solution, the solution was cloudy, opalescent upon being stirred, and of low viscosity and usually was thrown away. However, Kwolek persuaded the technician, Charles Smullen, who ran the spinneret, to test her solution and her supervisor and her laboratory director understood the significance of her accidental discovery and a new field of polymer chemistry quickly arose. By 1971, modern Kevlar was introduced, however, Kwolek was not very involved in developing the applications of Kevlar. Kevlar is synthesized in solution from the monomers 1, 4-phenylene-diamine, the result has liquid-crystalline behavior, and mechanical drawing orients the polymer chains in the fibers direction. Hexamethylphosphoramide was the solvent initially used for the polymerization, but for safety reasons, DuPont replaced it by a solution of N-methyl-pyrrolidone, as this process had been patented by Akzo in the production of Twaron, a patent war ensued. Kevlar production is expensive because of the difficulties arising from using concentrated sulfuric acid, needed to keep the water-insoluble polymer in solution during its synthesis and spinning. Several grades of Kevlar are available, Kevlar K-29 – in industrial applications, such as cables, asbestos replacement, brake linings, Kevlar K49 – high modulus used in cable and rope products. When Kevlar is spun, the fiber has a tensile strength of about 3,620 MPa. The polymer owes its high strength to the many inter-chain bonds and these inter-molecular hydrogen bonds form between the carbonyl groups and NH centers. Additional strength is derived from aromatic stacking interactions between adjacent strands, the presence of salts and certain other impurities, especially calcium, could interfere with the strand interactions and care is taken to avoid inclusion in its production. Kevlars structure consists of relatively rigid molecules tend to form mostly planar sheet-like structures rather like silk protein. Kevlar maintains its strength and resilience down to temperatures, in fact

10.
Jockey
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A jockey is someone who rides horses in horse racing or steeplechase racing, primarily as a profession. The word also applies to camel riders in camel racing, the word is by origin a diminutive of jock, the Northern English or Scots colloquial equivalent of the first name John, which is also used generically for boy, or fellow, at least since 1529. A familiar instance of the use of the word as a name is in Jockey of Norfolk in Shakespeares Richard III. v.3,304, the current usage which means a person who rides a horse in races was first seen in 1670. Another possible origin is the Gaelic word eachaidhe, a horseman, the Irish name Eochaid is related to each, horse, and is usually translated as horse rider. This is phonetically similar to jockey Jockeys must be light to ride at the weights which are assigned to their mounts. There are horse carrying weight limits, that are set by racing authorities, the Kentucky Derby, for example, has a weight limit of 126 lb including the jockeys equipment. The weight of a jockey usually ranges from 108 to 118 lb, despite their light weight, they must be able to control a horse that is moving at 40 mph and weighs 1,200 lb. Though there is no limit for jockeys, they are usually fairly short due to the weight limits. Jockeys typically stand around 4 ft 10 in to 5 ft 6 in, Jockeys are normally self employed, nominated by horse trainers to ride their horses in races, for a fee and a percentage of the purse winnings. In Australia, employment of apprentice jockeys is in terms of indenture to a master, Jockeys often cease their riding careers to take up other employment in racing, usually as trainers. In this way the system serves to induct young people into racing employment. Jockeys usually start out when they are young, riding work in the morning for trainers and it is normally necessary for an apprentice jockey to ride a minimum of about 20 barrier trials successfully before being permitted to ride in races. An apprentice jockey is known as a bug boy because the asterisk that follows the name in the program looks like a bug, all jockeys must be licensed and usually are not permitted to bet on a race. An apprentice jockey has a master, who is a horse trainer and this allowance is adjusted according to the number of winners that the apprentice has ridden. After a four-year indentured apprenticeship, the apprentice becomes a jockey and usually develops relationships with trainers. Sometimes senior jockeys are paid a retainer by an owner gives the owner the right to insist the jockey ride their horses in races. Racing modeled on the English Jockey Club spread throughout the world with colonial expansion, the colors worn by jockeys in races are the registered colors of the owner or trainer who employs them. The practice of riders wearing colors probably stems from medieval times when jousts were held between knights, however, the origins of racing colors of various patterns may have been influenced by racing held in Italian city communities since medieval times

11.
Horse racing
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Horse racing is an equestrian performance sport, typically involving two or more horses ridden by jockeys or driven over a set distance for competition. Horse races vary widely in format, often, countries have developed their own particular horse racing traditions. Variations include restricting races to particular breeds, running over obstacles, running over different distances, running on different track surfaces, Horse racing has a long and distinguished history and has been practised in civilisations across the world since ancient times. Archaeological records indicate that horse racing occurred in Ancient Greece, Babylon, Syria and it also plays an important part of myth and legend, such as the contest between the steeds of the god Odin and the giant Hrungnir in Norse mythology. Chariot racing was one of the most popular ancient Greek, Roman, both chariot and mounted horse racing were events in the ancient Greek Olympics by 648 BC and were important in the other Panhellenic Games. This was despite the fact that racing was often dangerous to both driver and horse as they frequently suffered serious injury and even death. In the Roman Empire, chariot and mounted horse racing were major industries, fifteen to 20 riderless horses, originally imported from the Barbary Coast of North Africa, ran the length of the Via del Corso, a long, straight city street, in about 2½ minutes. In later times, Thoroughbred racing became, and remains, popular with the aristocrats and royalty of British society, historically, equestrians honed their skills through games and races. Equestrian sports provided entertainment for crowds and honed the excellent horsemanship that was needed in battle, Horse racing of all types evolved from impromptu competitions between riders or drivers. The various forms of competition, requiring demanding and specialized skills from both horse and rider, resulted in the development of specialized breeds and equipment for each sport. The popularity of sports through the centuries has resulted in the preservation of skills that would otherwise have disappeared after horses stopped being used in combat. There are many different types of racing, including, Flat racing. Jump racing, or Jumps racing, also known as Steeplechasing or, in the UK and Ireland, National Hunt racing, Harness racing, where horses trot or pace while pulling a driver in a sulky. Breeds that are used for flat racing include the Thoroughbred, Quarter Horse, Arabian, Paint, Jump racing breeds include the Thoroughbred and AQPS. In harness racing, Standardbreds are used in Australia, New Zealand and North America, light cold blood horses, such as Finnhorses and Scandinavian coldblood trotter are also used in harness racing within their respective geographical areas. There also are races for ponies, both flat and jump and harness racing, Flat racing is the most common form of racing seen worldwide. Track surfaces vary, with turf most common in Europe, dirt more common in North America and Asia, individual flat races are run over distances ranging from 440 yards up to two and a half miles, with distances between five and twelve furlongs being most common. Short races are referred to as sprints, while longer races are known as routes in the United States or staying races in Europe

12.
Football helmet
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The football helmet is a piece of protective equipment used mainly in American football and Canadian football. It consists of a plastic shell with thick padding on the inside, a face mask made of one or more plastic-coated metal bars. Helmets are a requirement at all levels of organized football, except for variations such as flag football. Although they are protective, players can and do still suffer head injuries such as concussions, one of the first instances of football headgear dates to 1896 when Lafayette College halfback George Rose Barclay began to use straps and earpieces to protect his ears. It is not certain who invented the football helmet, reeves had been advised by a Navy doctor that another kick to his head would result in instant insanity or even death, so he commissioned an Annapolis shoemaker to make him a helmet out of leather. Later, helmets were made of padded leather and resembled aviators helmets or modern day scrum caps, at least in professional football, they were optional. Some National Football League players, notably Hall-of-Famer Bill Hewitt, played all or most of their careers without a helmet, one innovation from the early 1900s period was hardened leather. 1917 marked the first time helmets were raised above the head in an attempt to direct blows away from the top of the head, ear flaps also had their downfall during this period as they had little ventilation and made it difficult for players to hear. The 1920s marked the first time helmets were widely used in the sport of football. These helmets were made of leather and had some padding on the inside, in addition, they lacked face masks. As a result, injuries were very common, early helmets also absorbed a lot of heat, making them very uncomfortable to wear. In 1939, the Riddell Company of Chicago, Illinois started manufacturing plastic helmets because it felt that plastic helmets would be safer than those made of leather, plastic was found to be more effective because it held its shape when full collision contact occurred on a play. These helmets were also more comfortable and had more padding to cushion the head in an impact. Included with the helmet came plastic face mask, which allowed the helmet to protect the entire head. By the mid-1940s, helmets were required in the NFL and they were still made of leather, but with improved manufacturing techniques had assumed their more familiar spherical shape. By the 1950s, the introduction of polymers ended the leather helmet era, the NFL also recommended face masks for players in 1955, reducing the number of broken noses and teeth, but also necessitating new rules prohibiting opposing players from grabbing the face mask. Vin Ferrara, a former Harvard quarterback, accidentally discovered a new way to cushion football helmets, one night, Ferrara was looking for an aspirin when he saw a squirt bottle in his medicine cabinet. As he pumped it and then punched it, he realized that the bottle withstood the blows of different forces, Ferrara immediately came up with the idea to encase football helmets with a number of inflatable pockets in order to cushion the blows a football player receives to reduce concussions

13.
Hockey helmet
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A hockey helmet is worn by players of ice hockey, inline hockey, and bandy to help protect the head from potential injury when hit by the puck, sticks, skates, boards, other players, or the ice. Hockey helmets grip the head from inside by cupping the back of head, helmet manufacturers will have a chart that relates their helmet sizes to head measurements. Most helmets have tool-free adjustments, but on older models, the size is adjusted by loosening the screws on the side to slide the front portion forward or back. The first player to wear a helmet for protective purposes was George Owen. In 1927, Barney Stanley presented a prototype of a helmet at the NHLs annual meeting, helmets appeared after the Ace Bailey–Eddie Shore incident on December 12,1933, as a result of which Bailey almost died and Shore suffered a severe head injury. After that, Art Ross engineered a new design and when the Boston Bruins took to the ice in a game against the Ottawa Senators. Most Bruins players didnt wear the helmet after the game, with the exception of Eddie Shore, in the 1930s, the Toronto Maple Leafs players were ordered to add helmets to their equipment. A few minutes into the first game with the new helmets, the helmets were generally unpopular with fans, media, and other players. A few players, such as Des Smith, Bill Mosienko, Dit Clapper, during the Original Six era, Maurice Richard and Elmer Lach briefly wore helmets. Jack Crawford wore a helmet to hide his head and Charlie Burns wearing one to protect the metal plates in his head from an injury incurred in playing junior ice hockey. The death of Bill Masterton from an injury in a January 13,1968 in a game between the Minnesota North Stars and Oakland Seals started to change perceptions surrounding helmets. The 1972 Summit Series showcased an entirely helmet clad Soviet Union team, with Paul Henderson, Stan Mikita, usage increased to the point that 70% of NHL players were wearing them by 1979. In August 1979, then President of the National Hockey League, John Ziegler, the introduction of the helmet rule will be an additional safety factor, he said. The rule allowed players who signed contracts prior to June 1,1979 to continue to not wear a helmet provided a liability waiver was signed. The last player to play without a helmet was Craig MacTavish, a visor or shield in ice hockey is a device attached to the front of a helmet to reduce potential of injury to the face. Visors cover the half of the face, while full face shields cover the entire face. A series of eye injuries, most notably that to Bruce Fogarty, have led to a call from many to enforce their wearing, as of 2015, 89% of NHL players wear visors. Many other leagues around the world mandate the use of visors, visors and shields, made of a high impact-resistant plastic, offer better overall vision than the wire cages available, which can obscure vision in certain areas

14.
Cricket helmet
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In the sport of cricket, batsmen often wear a helmet to protect themselves from injury or concussion by the cricket ball, which is very hard and can be bowled to them at speeds over 90 miles per hour. Cricket helmets cover the whole of the skull, and have a grill or perspex visor to protect the face, fielders who are positioned very close to the batsman often wear a helmet and shin guards. Nowadays it is almost unheard of for a cricketer to face a fast bowler without a helmet. Some batsmen prefer not to wear a helmet when facing spin bowling, in under-18 cricket they are compulsory for all batsmen and any fielder within 15 yards of the bat. There are recorded instances of cricketers using towels, scarves and padded caps to protect themselves throughout cricket history, patsy Hendren was one of the first to use a self designed protective hat in the 1930s. Helmets were not in use until the 1970s. The first helmets were seen in World Series Cricket, with Dennis Amiss being the first player to wear a helmet. Mike Brearley was another player who wore his own design, tony Greig was of the opinion that they would make cricket more dangerous by encouraging bowlers to bounce the batsmen. Graham Yallop of Australia was the first to wear a helmet to a test match on 17 March,1978. Later Dennis Amiss of England popularised it in Test cricket, helmets began to be widely worn thereafter. The last batsmen at the highest level to never wear a helmet throughout his career was Viv Richards, batting helmet for baseball or softball

15.
Batting helmet
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A batting helmet is worn by batters in the game of baseball or softball. It is meant to protect the head from errant pitches thrown by the pitcher. A batter who is hit by pitch, due to an inadvertent wild pitch or a purposeful attempt to hit him, may be seriously, even fatally. In 1905, Mogridge created the first crude protective head gear and was granted patent No.780899 for a head protector and this first attempt at a batting helmet was said to look like an inflatable boxing glove that wrapped around the hitters head. Roger Bresnahan, Hall of Fame catcher who was injured after being struck in the head with a pitch, the helmets were not so much helmets as they were protective earmuffs. They did not protect the head of the batter but rather protected the ear. In 1914, minor leaguer Joe Bosk, playing for the Utica Utes, the first known case of a manager issuing head protectors to his players on a large scale was Philadelphia Phillies manager Pat Moran who gave cork-cushioned hats to his players in 1921. Despite the fatal beaning of Ray Chapman in 1920, protective headgear was used only rarely in the major leagues. Cochrane himself went on saying that players should absolutely be required to wear protective helmets. Only one week after Cochranes injury, on June 1,1937, managers of both teams decided to use batting practice as a test run for helmet use on their players, before a game between the two teams. Though there is evidence of the polo helmets being worn in batting practice. The first documented team to wear helmets in a game was the Des Moines Demons of the Western League and they also used polo helmets but the idea did not stick, as they only wore the helmets for one game. Buster Mills was the first player in the league to use a helmet, the idea of making helmets a required part of Major League Baseball was discussed by officials of the National League in a meeting at the 1940 MLB All-Star Game in Chicago. Ford Frick, president of the National League, showed the helmet he designed with the hopes that the league would adopt it. Though the National League at this meeting did not adopt it, in 1941, the National League adopted the use of a helmet, designed by George Bennett, a Johns Hopkins University brain surgeon, for use by all teams in spring training. On March 8,1941 the Brooklyn Dodgers announced that the players would be wearing the helmets during regular season games. On April 26,1941 the Washington Senators joined the Dodgers as the two teams to fully adopt the batting helmet for regular season use. The New York Giants on June 6 and the Chicago Cubs on June 24 also joined the list of teams to adopt the use of protective helmets during games

16.
Camogie
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Camogie is an Irish stick-and-ball team sport played by women, it is almost identical to the game of hurling played by men. Camogie is played by 100,000 women in Ireland and worldwide and it is organised by the Dublin-based Camogie Association or An Cumann Camógaíochta. The game consists of two 30 minute halves, matches are contested by two teams of 15 a side, using a field 130m to 145m long and 80m to 90m wide. H-shaped goals are used, a goal is equal to three points and a point is equal to one point. The annual All Ireland Camogie Championship has an attendance of 33,154 while average attendances in recent years are in the region of 15,000 to 18,000. The final is televised live, with a TV audience of over 300,000 being claimed, the rules are almost identical to hurling, with a few exceptions. Goalkeepers wear the colours as outfield players. This is because no special rules apply to the goalkeeper and so there is no need for officials to differentiate between goalkeeper and outfielders, a camogie player can handpass a score Camogie games last 60 minutes, two 30-minute halves. Ties are resolved by multiple 2×10-minute sudden death extra time periods, in these, dropping the camogie stick to handpass the ball is permitted. A smaller sliotar is used in camogie – commonly known as a size 4 sliotar – whereas hurlers play with a size 5 sliotar. If a defending player hits the sliotar wide, a 45-metre puck is awarded to the opposition After a score, the metal band on the camogie stick must be covered with tape. Two points are awarded for a direct from a sideline cut. Camogie players must wear skirts or skorts rather than shorts, experimental rules were drawn up in 1903 for a female stick-and-ball game by Máire Ní Chinnéide, Seán Ó Ceallaigh, Tadhg Ó Donnchadha and Séamus Ó Braonáin. The Official Launch of Camogie took place with the first public match between Craobh an Chéitinnigh and Cúchulainns on 17 July at a Feis in Navan, the sports governing body, the Camogie Association or An Cumann Camógaíochta was founded in 1905 and re-constituted in 1911,1923 and 1939. Until June 2010 it was known as Cumann Camógaíochta na nGael, thus, although camogie was founded by women, and independently run, there was, from the outset, a small yet powerful male presence within its administrative ranks. Of all the cultural nationalist organisations for adults that emerged during the fin de siècle, under Séamus Ó Braonáins original 1903 camogie rules both the match and the field were shorter than their hurling equivalents. Matches were 40 minutes, increased to 50 minutes in 1934, in 1999 camogie moved to the GAA field-size and 15-a-side, adopting the standard GAA butterfly formation. The name was invented by Tadhg Ua Donnchadha at meetings in 1903 in advance of the first matches in 1904, men play using a curved stick called in Irish a camán

17.
Hurling
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Hurling, is an outdoor team game of ancient Gaelic and Irish origin, administered by the Gaelic Athletic Association. The game has prehistoric origins, and has played for 3,000 years. One of Irelands native Gaelic games, it shares a number of features with Gaelic football, such as the field and goals, the number of players, there is a similar game for women called camogie. It shares a common Gaelic root with the sport of shinty, the sliotar can be caught in the hand and carried for not more than four steps, struck in the air, or struck on the ground with the hurley. It can be kicked, or slapped with a hand for short-range passing. A player who wants to carry the ball for more than four steps has to bounce or balance the sliotar on the end of the stick, no protective padding is worn by players. A plastic protective helmet with a faceguard is mandatory for all age groups, including senior level, the game has been described as a bastion of humility, with player names absent from jerseys and a players number decided by his position on the field. Hurling is played throughout the world, and is popular among members of the Irish diaspora in North America, Europe, Australia, New Zealand, South Africa and Argentina, in many parts of Ireland, however, hurling is a fixture of life. It has featured regularly in art such as film, music. A team comprises 15 players, or hurlers, the hurley is generally 24 to 36 inches in length. The ball, known as a sliotar, has a cork centre, the goalkeepers hurley usually has a bas twice the size of other players hurleys to provide some advantage against the fast moving sliotar. A good strike with a hurley can propel the ball over 150 km/h in speed and 110 metres in distance, a ball hit over the bar is worth one point. A ball that is hit under the bar is called a goal and is three points. As of 2010, all players must wear a helmet, a hurling pitch is similar in some respects to a rugby pitch but larger. The grass pitch is rectangular, stretching 130–145 metres long and 80–90 m wide. There are H-shaped goalposts at each end, formed by two posts, which are usually 6–7 metres high, set 6.5 m apart, a net extending behind the goal is attached to the crossbar and lower goal posts. The same pitch is used for Gaelic football, the GAA, lines are marked at distances of 14 yards,21 yards and 65 yards from each end-line. Shorter pitches and smaller goals are used by youth teams, teams consist of fifteen players, a goalkeeper, three full backs, three half backs, two midfielders, three half forwards and three full forwards

18.
Rock climbing
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Rock climbing is an activity in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a usually pre-defined route without falling. Due to the length and extended endurance required and because accidents are likely to happen on descent than ascent. It is very rare for a climber to downclimb, especially on the larger multiple pitches, professional Rock climbing competitions have the objectives of either completing the route in the quickest possible time or attaining the farthest point on an increasingly difficult route. Scrambling, another activity involving the scaling of hills and similar formations, is similar to rock climbing, however, rock climbing is generally differentiated by its sustained use of hands to support the climbers weight as well as to provide balance. Rock climbing is a physically and mentally demanding sport, one that often tests a climbers strength, endurance, agility and it can be a dangerous activity and knowledge of proper climbing techniques and usage of specialized climbing equipment is crucial for the safe completion of routes. Because of the range and variety of rock formations around the world. Paintings dating from 200 BC show Chinese men rock climbing China woop woop, in early America, the cliff-dwelling Anasazi in the 12th century were thought to be excellent climbers. Early European climbers used rock climbing techniques as a required to reach the summit in their mountaineering exploits. In the 1880s, European rock climbing become an independent pursuit outside of mountain climbing, Rock climbing evolved gradually from an alpine necessity to a distinct athletic activity. However, climbing techniques, equipment and ethical considerations have evolved steadily, today, free climbing, climbing using holds made entirely of natural rock while using gear solely for protection and not for upward movement, is the most popular form of the sport. Free climbing has since divided into several sub-styles of climbing dependent on belay configuration. Over time, grading systems have also created in order to compare more accurately the relative difficulties of the rock climbs. In How to Rock Climb, John Long notes that for moderately skilled climbers simply getting to the top of a route is not enough, in rock climbing, style refers to the method of ascending the cliff. There are three styles of climbing, on-sight, flash, and redpoint. To on-sight a route is to ascend the wall without aid or any foreknowledge and it is considered the way to climb with the most style. Flashing is similar to on-sighting, except that the climber has previous information about the route including talking about the beta with other climbers, redpointing means to make a free ascent of the route after having first tried it. Free climbing is typically divided into styles that differ from one another depending on the choice of equipment used

19.
Construction
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Construction is the process of constructing a building or infrastructure. Construction as an industry comprises six to nine percent of the domestic product of developed countries. Construction starts with planning, design, and financing, and continues until the project is built, large-scale construction requires collaboration across multiple disciplines. An architect normally manages the job, and a manager, design engineer. For the successful execution of a project, effective planning is essential, the largest construction projects are referred to as megaprojects. Construction is a term meaning the art and science to form objects, systems, or organizations. Construction is used as a verb, the act of building, and a noun, how a building was built, in general, there are three sectors of construction, buildings, infrastructure and industrial. Building construction is further divided into residential and non-residential. Infrastructure is often called heavy/highway, heavy civil or heavy engineering and it includes large public works, dams, bridges, highways, water/wastewater and utility distribution. Industrial includes refineries, process chemical, power generation, mills, there are other ways to break the industry into sectors or markets. Engineering News-Record is a magazine for the construction industry. Each year, ENR compiles and reports on data about the size of design and they publish a list of the largest companies in the United States and also a list the largest global firms. In 2014, ENR compiled the data in nine market segments and it was divided as transportation, petroleum, buildings, power, industrial, water, manufacturing, sewer/waste, telecom, hazardous waste plus a tenth category for other projects. In their reporting on the Top 400, they used data on transportation, sewer, hazardous waste, the Standard Industrial Classification and the newer North American Industry Classification System have a classification system for companies that perform or otherwise engage in construction. To recognize the differences of companies in this sector, it is divided into three subsectors, building construction, heavy and civil engineering construction, and specialty trade contractors, there are also categories for construction service firms and construction managers. Building construction is the process of adding structure to real property or construction of buildings, the majority of building construction jobs are small renovations, such as addition of a room, or renovation of a bathroom. Often, the owner of the property acts as laborer, paymaster, for this reason, those with experience in the field make detailed plans and maintain careful oversight during the project to ensure a positive outcome. Residential construction practices, technologies, and resources must conform to local building authority regulations, materials readily available in the area generally dictate the construction materials used

20.
Mining
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Mining is extraction of valuable minerals or other geological materials from the earth usually from an orebody, lode, vein, seam, reef or placer deposits. These deposits form a mineralized package that is of economic interest to the miner, ores recovered by mining include metals, coal, oil shale, gemstones, limestone, chalk, dimension stone, rock salt, potash, gravel, and clay. Mining is required to obtain any material that cannot be grown through agricultural processes, Mining in a wider sense includes extraction of any non-renewable resource such as petroleum, natural gas, or even water. Mining of stones and metal has been a human activity since pre-historic times, Mining operations usually create a negative environmental impact, both during the mining activity and after the mine has closed. Hence, most of the nations have passed regulations to decrease the impact. Work safety has long been a concern as well, and modern practices have significantly improved safety in mines, levels of metals recycling are generally low. Unless future end-of-life recycling rates are stepped up, some rare metals may become unavailable for use in a variety of consumer products, due to the low recycling rates, some landfills now contain higher concentrations of metal than mines themselves. Since the beginning of civilization, people have used stone, ceramics and, later and these were used to make early tools and weapons, for example, high quality flint found in northern France, southern England and Poland was used to create flint tools. Flint mines have been found in areas where seams of the stone were followed underground by shafts. The mines at Grimes Graves and Krzemionki are especially famous, other hard rocks mined or collected for axes included the greenstone of the Langdale axe industry based in the English Lake District. The oldest-known mine on archaeological record is the Lion Cave in Swaziland, at this site Paleolithic humans mined hematite to make the red pigment ochre. Mines of an age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons. Ancient Egyptians mined malachite at Maadi, at first, Egyptians used the bright green malachite stones for ornamentations and pottery. Later, between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were found at Wadi Hammamat, Tura, Aswan and various other Nubian sites on the Sinai Peninsula. Mining in Egypt occurred in the earliest dynasties, the gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by the Greek author Diodorus Siculus, who mentions fire-setting as one used to break down the hard rock holding the gold. One of the complexes is shown in one of the earliest known maps, the miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust

21.
Motorcycle helmet
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A motorcycle helmet is a type of helmet used by motorcycle riders. The primary goal of a helmet is motorcycle safety - to protect the riders head during impact, thus preventing or reducing head injury. Some helmets provide additional conveniences, such as ventilation, face shields, ear protection, motorcyclists are at high risk in traffic crashes. A2008 systematic review examined studies on motorcycle riders who had crashed and looked at use as an intervention. The review concluded that helmets reduce the risk of injury by around 69%. He got a Mr Moss of Bethnal Green to make canvas and shellac helmets stiff enough to stand a heavy blow and smooth enough to glance off any projections it encountered. Gardner took 94 of these helmets with him to the Isle of Man, dr Gardner received a letter later from the Isle of Man medical officer stating that after the T. T. they normally had several interesting concussion cases but that in 1914 there was none. In May 1935, T. E. Lawrence had a crash on a Brough Superior SS100 on a road near his cottage near Wareham. The accident occurred because a dip in the road obstructed his view of two boys on bicycles, swerving to avoid them, Lawrence lost control and was thrown over the handlebars. He was not wearing a helmet, and suffered head injuries which left him in a coma. Cairns research led to the use of crash helmets by both military and civilian motorcyclists. There are five types of helmets intended for motorcycling, and others not intended for motorcycling. Many full face helmets include vents to increase the airflow to the rider, the significant attraction of these helmets is their protectiveness. Some wearers dislike the increased heat, sense of isolation, lack of wind, studies have shown that full face helmets offer the most protection to motorcycle riders because 35% of all crashes showed major impact on the chin-bar area. Wearing a helmet with less coverage eliminates that protection — the less coverage the helmet offers, the visor allows the rider to dip his or her head and provide further protection from flying debris during off road riding. It also serves the purpose of shielding the wearers eyes from the sun. Modern off-road helmets include a bar to provide some facial impact protection in addition to protection from flying dirt. When properly combined with goggles, the result provides most of the protective features of full face street helmets

22.
Resin
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In polymer chemistry and materials science, resin is a solid or highly viscous substance of plant or synthetic origin that is typically convertible into polymers. They are often mixtures of compounds, principally terpenes. Many plants, particularly woody plants, produce resin in response to injury, the resin acts as a bandage protecting the plant from invading insects and pathogens. Plants secrete resins and rosins for their protective benefits, the resin produced by most plants is composed mainly of terpenes and derivatives. Some resins also contain a proportion of resin acids. The individual components of resin can be separated by fractional distillation, rosins on the other hand are less volatile and consist, inter alia, of diterpenes. Amber is fossil resin from coniferous and other tree species, copal, kauri gum, dammar and other resins may also be found as subfossil deposits. Subfossil copal can be distinguished from genuine fossil amber because it becomes tacky when a drop of a solvent such as acetone or chloroform is placed on it, african copal and the kauri gum of New Zealand are also procured in a semi-fossil condition. Solidified resin from which the volatile terpene components have been removed by distillation is known as rosin, typical rosin is a transparent or translucent mass, with a vitreous fracture and a faintly yellow or brown colour, non-odorous or having only a slight turpentine odor and taste. Rosin is insoluble in water, mostly soluble in alcohol, essential oils, ether and hot fatty oils, and softens and melts under the influence of heat, rosin consists of a complex mixture of different substances including organic acids named the resin acids. These are closely related to the terpenes, and derive from them through partial oxidation, Resin acids can be dissolved in alkalis to form resin soaps, from which the purified resin acids are regenerated by treatment with acids. Examples of resin acids are abietic acid, C20H30O2, plicatic acid contained in cedar, and pimaric acid, C20H30O2, a constituent of galipot resin. Abietic acid can also be extracted from rosin by means of hot alcohol, it crystallizes in leaflets, pimaric acid closely resembles abietic acid into which it passes when distilled in a vacuum, it has been supposed to consist of three isomers. Rosin is obtained from pines and some plants, mostly conifers. Propolis, consisting largely of resins collected from such as poplars and conifers, is used by honey bees to seal gaps in their hives. Shellac and lacquer are examples of insect-derived resins, asphaltite and Utah resin are petroleum bitumens, not a product secreted by plants, although it was ultimately derived from plants. These were highly prized substances, and required as incense in religious rites. The word resin has been applied in the world to nearly any component of a liquid that will set into a hard lacquer or enamel-like finish

23.
Plastic
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Plastic is a material consisting of any of a wide range of synthetic or semi-synthetic organic compounds that are malleable and can be molded into solid objects. Plastics are typically organic polymers of high mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, due to their relatively low cost, ease of manufacture, versatility, and imperviousness to water, plastics are used in an enormous and expanding range of products, from paper clips to spaceships. They have already displaced many traditional materials, such as wood, stone, horn and bone, leather, paper, metal, glass, and ceramic, in most of their former uses. In developed countries, about a third of plastic is used in packaging, other uses include automobiles, furniture, and toys. In the developing world, the ratios may be different - for example, the worlds first fully synthetic plastic was bakelite, invented in New York in 1907 by Leo Baekeland who coined the term plastics. Toward the end of the century, one approach to this problem was met with wide efforts toward recycling, the word plastic is derived from the Greek πλαστικός meaning capable of being shaped or molded, from πλαστός meaning molded. The common word plastic should not be confused with the technical adjective plastic, used for insulating parts in electrical fixtures, paper laminated products, thermally insulation foams. Problems include the probability of moldings naturally being dark colors, One of the most expensive commercial polymers. It forms the basis of artistic and commercial acrylic paints when suspended in water with the use of other agents, polytetrafluoroethylene – Heat-resistant, low-friction coatings, used in things like non-stick surfaces for frying pans, plumbers tape and water slides. It is more known as Teflon. Urea-formaldehyde – One of the aminoplasts and used as an alternative to phenolics. Used as an adhesive and electrical switch housings. Early plastics were bio-derived materials such as egg and blood proteins, in 1600 BC, Mesoamericans used natural rubber for balls, bands, and figurines. Treated cattle horns were used as windows for lanterns in the Middle Ages, materials that mimicked the properties of horns were developed by treating milk-proteins with lye. In the 1800s, as industrial chemistry developed during the Industrial Revolution, the development of plastics also accelerated with Charles Goodyears discovery of vulcanization to thermoset materials derived from natural rubber. Parkesine is considered the first man-made plastic, the plastic material was patented by Alexander Parkes, In Birmingham, UK in 1856. It was unveiled at the 1862 Great International Exhibition in London, parkesine won a bronze medal at the 1862 Worlds fair in London

24.
Great helm
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They were used by knights in most European armies between about 1220 to 1540 AD. In its simplest form, the helm was a flat-topped cylinder of steel that completely covered the head and had only very small openings for the eyes. Later designs gained more of a design, particularly on the top. The great helm ultimately evolved from the helmet, which had been produced in a flat-topped variant with a square profile by about 1180. From this type of helmet an intermediate type, called an enclosed helmet or primitive great helm, in this helmet the expansion of the nasal produced a full face-plate, pierced for sight and breathing. This helmet was largely superseded by the great helm by c. A later variant with a conical top is known as a sugarloaf helm. In Spanish they are called yelmo de Zaragoza, referring to Zaragoza where they were introduced for the first time in the Iberian peninsula, knights usually wore the great helm over a mail coif sometimes in conjunction with a close-fitting iron skull cap known as a cervelliere. The bascinet had a mail curtain attached, a camail or aventail, mail throat and neck defences such as these were made obsolete when plate gorgets were introduced, around 1400. The bascinet evolved from its early skull cap form to supersede the great helm for combat, the great helm fell into disuse during the 15th century, however it was used commonly in tournaments where a version of the great helm, the frog-mouthed tilting helm, evolved. The great helm is today especially popular amongst live-action role players and it is inexpensive, easy to manufacture with even rudimentary equipment, and provides good protection for the head against both sharp and blunt weapons. Its biggest drawbacks are poor ventilation and air circulation, especially if worn with closed-cell foam padding, making it hot in warm weather. Modern reenactment versions of great helms weigh 1.5 to 3 kg, for safety reasons, they are made from thicker steel than medieval originals but are not overly heavy, cumbersome, or uncomfortable. Although visor slits are usually only some 20–30 mm wide, they do not greatly restrict the field of vision as they are close to the wearers eyes. Gravett, Christopher Norman Knight 950-1204 AD, Osprey, London, archived from the original on 2011-04-01

25.
Aventail
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An aventail or camail is a flexible curtain of mail attached to the skull of a helmet that extends to cover the throat, neck and shoulders. Part or all of the face, with spaces to allow vision, the earliest camails were riveted directly to the edge of the helmet, however, beginning in the 1320s in Western Europe a detachable version replaced this type. The detachable aventail was attached to a band, which was in turn attached to the lower border of the helmet by a series of staples called vervelles. Holes in the band were passed over the vervelles. Aventails were most commonly seen on bascinets in the 14th century, some aventails were decorated with edging in brass or bronze links, or with a zig-zag lower edge. By the mid 14th century, the aventail had replaced the mail coif completely, the Routledge Companion to Medieval Warfare. Knight, Noble Warrior of England 1200–1600

26.
Neurosurgery
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In different countries, there are different requirements for an individual to legally practice neurosurgery, and there are varying methods through which they must be educated. In most countries, neurosurgeon training requires a period of seven years after graduating from medical school. In the United States, a neurosurgeon must generally complete four years of education, four years of medical school. Most, but not all, residency programs have some component of science or clinical research. Neurosurgeons may pursue training in the form of a fellowship, after residency or in some cases. In the U. S. neurosurgery is considered a highly competitive specialty composed of 0. 6% of all practicing physicians, in the United Kingdom, students must gain entry into medical school. MBBS qualification takes four to six years depending on the students route, junior doctors then apply to enter the neurosurgical pathway. Neurosurgery remains consistently amongst the most competitive specialties in which to obtain entry. The Incas appear to have practiced a procedure known as trepanation since the late Stone age, during the Middle Ages in Arabia from 936 to 1013 AD, Al-Zahrawi performed surgical treatments of head injuries, skull fractures, spinal injuries, hydrocephalus, subdural effusions and headache. There was not much advancement in neurosurgery until late 19th early 20th century, history of electrodes in the brain, In 1878 Richard Canton discovered that electrical signals transmitted through an animals brain. In 1950 Dr. Jose Delgado invented the first electrode that was implanted in a brain, using it to make it run. In 1972 the cochlear implant, a neurological prosthetic that allowed people to hear was marketed for commercial use. In 1998 researcher Philip Kennedy implanted the first Brain Computer Interface into a human subject, history of tumor removal, In 1879 after locating it via neurological signs alone, Scottish surgeon William Macewen performed the first successful brain tumor removal. On March 16,1907 Austrian surgeon Hermann Schloffer became the first to remove a pituitary tumor. The main advancements in neurosurgery came about as a result of highly crafted tools, modern neurosurgical tools, or instruments, include chisels, curettes, dissectors, distractors, elevators, forcepts, hooks, impactors, probes, suction tubes, power tools, and robots. Most of these tools, like chisels, elevators, forcepts, hooks, impactors. The main difference of these tools, pre and post advancement in neurosurgery, were the precision in which they were crafted and these tools are crafted with edges that are within a millimeter of desired accuracy. Other tools such as hand held power saws and robots have only recently been used inside of a neurological operating room

27.
Rock-climbing equipment
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A wide range of equipment is used during rock or any other type of climbing. The most popular types of climbing equipment are briefly described in this article, the article on protecting a climb describes equipment commonly used to protect a climber against the consequences of a fall. See also the Glossary of climbing terms for more equipment descriptions, climbing ropes are typically of kernmantle construction, consisting of a core of long twisted fibres and an outer sheath of woven coloured fibres. The core provides about 80% of the strength, while the sheath is a durable layer that protects the core. Ropes used for climbing can be divided into two classes, dynamic ropes and low elongation ropes, dynamic ropes are designed to absorb the energy of a falling climber, and are usually used as Belaying ropes. When a climber falls, the rope stretches, reducing the force experienced by the climber, their belayer. Low elongation ropes stretch much less, and are used in anchoring systems. They are also used for abseiling and as fixed ropes climbed with ascenders, modern webbing or tape is made of nylon or Spectra/Dyneema, or a combination of the two. Climbing-specific nylon webbing is generally tubular webbing, that is, it is a tube of nylon pressed flat and it is very strong, generally rated in excess of 9 kN, or about 2,020 pounds of force. Dyneema is even stronger, often rated above 20 kN and as high as 27 kN, in 2010, UK-based DMM performed fall factor 1 and 2 tests on various Dyneema and Nylon webbings, showing Dyneema slings can fail even under 60 cm falls. Tying knots in Dyneema webbing was proven to have reduced the amount of supported force by as much as half. When webbing is sewn or tied together at the ends, it becomes a sling or runner and these loops are made one of two ways—sewn or tied. Both ways of forming runners have advantages and drawbacks, and it is for the climber to choose which to use. Generally speaking, most climbers carry a few of both types and it is also important to note that only nylon can be safely knotted into a runner, Dyneema is always sewn because the fibers are too slippery to hold a knot under weight. Webbing has many such as, Extending the distance between protection and a tie-in point. An anchor around a tree or rock, protecting a rope that hangs over a sharp edge. Carabiners are metal loops with spring-loaded gates, used as connectors, once made primarily from steel, almost all carabiners for recreational climbing are now made from a light weight aluminum alloy. Steel carabiners are much heavier, but harder wearing, and therefore are used by instructors when working with groups

28.
Visor
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A visor is a surface that protects the eyes, such as shading them from the sun or other bright light or protecting them from objects. A type of headgear consisting only of a visor and a band as a way to fasten it around the head, any such vertical surface on any hat or helmet. Any such horizontal surface on any hat or helmet, a device in an automobile that the driver or front passenger can lower over part of the windshield to block the sun

29.
Goggles
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Goggles or safety glasses are forms of protective eyewear that usually enclose or protect the area surrounding the eye in order to prevent particulates, water or chemicals from striking the eyes. They are used in laboratories and in woodworking. They are often used in sports as well, and in swimming. Goggles are often worn when using tools such as drills or chainsaws to prevent flying particles from damaging the eyes. Many types of goggles are available as prescription goggles for those with vision problems, the Inuit and Yupik people carved Inuit snow goggles from caribou antler, wood, and shell to help prevent snow blindness. The goggles were curved to fit the users face and had a groove cut in the back to allow for the nose. A long thin slit was cut through the goggles to allow in an amount of light. The goggles were held to the head by a made of caribou sinew. In the early 20th century, goggles were worn by drivers of uncovered cars to prevent irritation of the eyes by dust or wind, the first pilot to wear goggles was probably Charles Manly in his failed attempt to fly Samuel Langleys aerodrome in 1903. The requirements for goggles varies depending on the use, some examples, Cold weather, Most modern cold-weather goggles have two layers of lens to prevent the interior from becoming foggy. With only a lens, the interior water vapor condenses onto the lens because the lens is colder than the vapor. The reasoning behind dual layer lens is that the lens will be warm while the outer lens will be cold. As long as the temperature of the lens is close to that of the interior water vapor. Swimming, Must be watertight to prevent water, such as water when swimming in the ocean, or chlorinated water when swimming in a pool. Allows swimmers to see clearly underwater and they will not be usable more than a few feet underwater, because the water pressure will press them tightly against the face. Examples of these include the Swedish goggles, power tools, Must be made of an unbreakable material that prevents chunks of metal, wood, plastic, concrete, and so on from hitting or piercing the eye. Usually has some sort of ventilation to prevent sweat from building up inside the goggles, blowtorch goggles, These protect the eyes from glare and flying sparks and hot metal splashes while using or near a blowtorch. They are not the filters for arc welding

30.
Helmet
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A helmet is a form of protective gear worn to protect the head from injuries. More specifically, a helmet aids the skull in protecting the human brain, ceremonial or symbolic helmets without protective function are sometimes used. The oldest known use of helmets was by Assyrian soldiers in 900 BC, soldiers still wear helmets, now often made from lightweight plastic materials. In civilian life, helmets are used for activities and sports, dangerous work activities. Since the 1990s, most helmets are made from resin or plastic, the word helmet is diminutive from helm, a medieval word for protective combat headgear. The Medieval great helm covers the head and often is accompanied with camail protecting throat. Originally a helmet was a helm which covered the head only partly, all helmets attempt to protect the users head by absorbing mechanical energy and protecting against penetration. Their structure and protective capacity are altered in high-energy impacts, beside their energy-absorption capability, their volume and weight are also important issues, since higher volume and weight increase the injury risk for the users head and neck. Anatomical helmets adapted to the head structure were invented by neurosurgeons at the end of the 20th century. Helmets used for different purposes have different designs, for example, a bicycle helmet must protect against blunt impact forces from the wearers head striking the road. A helmet designed for rock climbing must protect against heavy impact, sports helmets may have an integrated metal face protector. Baseball batting helmets have an expanded protection over the ear, which protects the jaw from injury, motorcycle helmets often have flip-down face screens for rain and wind protection, and they may also have projecting visors to protect the eyes from glare. Hard hats for construction workers are mainly to protect the wearer from falling objects such as tools. Helmets for riot police often have flip-down clear visors and thick padding to protect the back of the neck, Modern firefighters helmets protect the face and back of the head against impact, fires and electricity, and can include masks, communication systems, and other accessories. Welding helmets protect the eyes and face and neck from flash burn, ultraviolet light, sparks and heat. They have a window, called a lens shade, through which the welder looks at the weld. People with some medical conditions must wear a helmet to protect the brain, due to a gap in the braincase, mixed martial arts helmets have ear pads to prevent serious injuries to the athletes, who do not usually endure such force to the ears. Crash helmets for F1 racing drivers, their design and construction have evolved enormously, nevertheless, head and neck trauma remains the greatest single injury risk to drivers

31.
Ear plug
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An earplug is a device that is meant to be inserted in the ear canal to protect the users ears from loud noises or the intrusion of water, foreign bodies, dust or excessive wind. Some earplugs are designed to keep water out of the ear canal, especially during swimming. This type of earplug may be made of wax or moldable silicone which is custom-fitted to the ear canal by the wearer, exostosis, or Surfers ear, is a condition which affects people who spend large amounts of time in water in cold climates. Custom-fitted surfers earplugs help reduce the amount of water and wind that is allowed to enter the external ear canal and, thus. Jacques-Yves Cousteau warned that earplugs are harmful to divers, especially scuba divers, scuba divers breathe compressed air or other gas mixtures at a pressure matching the water pressure. This pressure is also inside the ear, but not between the eardrum and the earplug, so the pressure behind the eardrum will often burst the eardrum, skin divers have less pressure inside the ears, but they also have only atmospheric pressure in the outer ear canal. The PADI advises in the Open Water Diver Manual that only vented earplugs designed for diving should be used in diving, custom molded earplugs, made from a mold of the wearers ear and designed to precisely fit all ear canal shapes. Custom molded is further divided into laboratory-made and formed in place NIOSH Mining Safety and Health Research recommends using the roll, pull, and hold method when using memory foam earplugs. The process involves the rolling the earplug into a thin rod, pulling back on the ear. To get a seal, the user must wait about 20 to 30 seconds for the earplug to expand inside the canal. Furthermore, they may be disposable or reusable, with foam. Custom molded are non-disposable and made from acrylic, vinyl. Custom molded come as either vented or non-vented, a variation of the traditional foam earplug is the no-roll foam earplug that uses a built-in central stem to push the foam plugs into the ears. These earplugs achieve a seal due to their shape, rather than expansion after being rolled. These include the NIOSH HPD Well-Fit, as well as the Howard Leight VeriPro, Earplugs are especially useful to people exposed to excessively noisy devices or environments. The first recorded mention of the use of earplugs is in the Greek tale Odyssey, circe, their hostess, tells them of the Sirens bewitching song that makes men drive their boats ashore and perish. She advised Odysseus to fashion earplugs for his men from beeswax so they would not be lured to their deaths by the sirens song, in 1907, the German company Ohropax, which would produce mainly wax earplugs, was started by German inventor Max Negwer. Ray and Cecilia Benner invented the first mouldable pure silicone ear plugs in 1962, the earplugs were valued by swimmers, as well as those trying to avoid harmful noise, for their waterproof qualities

32.
Body armor
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Body armor or Body armour, or personal armor/armour is protective clothing, designed to absorb and/or deflect slashing, bludgeoning and penetrating attacks by weapons. It was historically used to military personnel, whereas today, it is also used to protect various types of police, private citizens. Many factors have affected the development of personal armor throughout human history, significant factors in the development of armor include the economic and technological necessities of armor production. For instance full plate armor first appeared in Medieval Europe when water-powered trip hammers made the formation of plates faster and cheaper, with the development of capitalism and technological advancements armor became more available to the lower classes often at a cost of quality. Eastern armor has a history, spanning several thousand years. The oldest known Western armor is the Dendra panoply, dating from the Mycenaean Era around 1400 BC, mail, also referred to as chainmail, is made of interlocking iron rings, which may be riveted or welded shut. It is believed to have been invented by Celtic people in Europe about 500 BC, most cultures who used mail used the Celtic word Byrnne or a variant, suggesting the Celts as the originators. The Romans widely adopted mail as the lorica hamata, although they made use of lorica segmentata. While no non-metallic armor survives, a linen laminate known as linothorax is repeatedly mentioned in ancient Greek sources, in East Asian history laminated armor such as lamellar, and styles similar to the coat of plates, and brigandine were commonly used. Later cuirasses and plates were also used, in pre-Qin dynasty times, leather armor was made out of rhinoceros. Chinese influence in Japan would result in the Japanese adopting Chinese styles, gradually, small additional plates or discs of iron were added to the mail to protect vulnerable areas. By the late 13th century, the knees were capped, a variety of methods for improving the protection provided by mail were used as armorers seemingly experimented. Hardened leather and splinted construction were used for arm and leg pieces, the coat of plates was developed, an armor made of large plates sewn inside a textile or leather coat. Early plate in Italy, and elsewhere in the 13th to 15th centuries were made of iron, Iron armor could be carburized or case hardened to give a surface of harder steel. Mail continued to be used to protect those joints which could not be protected by plate, such as the armpit, crook of the elbow. Another advantage of plate was that a lance rest could be fitted to the breast plate, the small skull cap evolved into a bigger true helmet, the bascinet, as it was lengthened downward to protect the back of the neck and the sides of the head. Additionally, several new forms of fully enclosed helmets were introduced in the late 14th century to replace the great helm, such as the sallet and barbute and later the armet and close helm. By about 1400 the full harness of plate armor had been developed in armories of Lombardy Heavy cavalry dominated the battlefield for centuries in part because of their armor

33.
Hard hat
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Suspension bands inside the helmet spreads the helmets weight and the force of any impact over the top of the head. Some helmet shells have a mid-line reinforcement ridge to improve impact resistance, the rock climbing helmet fulfills a very similar role in a different context and has a very similar design. A bump cap is a hard hat using a simplified suspension or padding. In the United States, the E. D, Bullard Company was a mining equipment firm in California created by Edward Dickinson Bullard in 1898, a veteran of the industrial safety business for 20 years. The company sold protective hats made of leather and his son, E. W. Bullard, returned home from World War I with a steel helmet that provided him with ideas to improve industrial safety. In 1919 Bullard patented a hard-boiled hat made of steamed canvas, glue and that same year, the U. S. Navy commissioned Bullard to create a shipyard protective cap that began the widespread use of hard hats. Not long after, Bullard developed a suspension to provide a more effective hat. These early designs bore a resemblance to the military M1917 Brodie helmet that served as their inspiration, on the Hoover Dam project in 1931, hard hat use was mandated by Six Companies, Inc. In 1933, construction began on the Golden Gate Bridge in San Francisco California, construction workers were required to wear hard hats, by order of Joseph Strauss, project chief engineer. Strauss strove to create a workplace, hence, he installed safety nets. Strauss also asked Bullard to create a hat to protect workers who performed sandblasting. Bullard produced a design that covered the face, provided a window for vision. In those times many workmens safety helmets were made of steel, aluminum became a standard for hard hats around 1938, except for electrical applications. MSA introduced the new plastic Skullgard Helmet in 1930 for the industry to withstand radiant heat loads of up to 350 °F. New plastic Bakelite was used to provide protection rigid enough to withstand hard sudden impacts within a high-heat environment, machinery of the times required that helmet materials used be electrically non-conducting. Bakelite resin compounded with wire screen and linen, the Skullgard Helmet is still manufactured, MSA also produced a low-crown version for coal miners known as Comfo-Cap Headgear. Fiberglass came into use in the 1940s, thermoplastics took over in the 1950s, as they are easy to mold and shape with heat and cost less to manufacture. In 1952, MSA offered the Shockgard Helmet to protect electrical linemen from electrical shock of up to 10,000 volts, in 1961, MSA released the Topgard Helmet, the first polycarbonate hard hat

34.
Riot police
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Riot police are police who are organized, deployed, trained or equipped to confront crowds, protests or riots. Riot police may be regular police who act in the role of police in particular situations or they may be separate units organized within or in parallel to regular police forces. Riot police are used in a variety of different situations and for a variety of different purposes and they may be employed to control riots as their name suggests, to disperse or control crowds, to maintain public order or discourage criminality, or to protect people or property. In some cases, riot police may function as a tool of repression by violently breaking up protests. In recent decades, observers have noted the increasing militarization of riot and protest policing, with police deploying snipers, flashbang grenades, riot police often use special equipment termed riot gear to help protect themselves and attack others. Riot gear typically includes personal armor, batons, riot shields, many riot police teams also deploy specialized less-than-lethal weapons, such as pepper spray, tear gas, rifles that fire rubber bullets, stun grenades, and Long Range Acoustic Devices

35.
Arc welding
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Arc welding is a process that is used to join metal to metal by using electricity to create enough heat to melt metal, and the melted metals when cool result in a binding of the metals. It is a type of welding that uses a power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes, the welding region is usually protected by some type of shielding gas, vapor, or slag. Arc welding processes may be manual, semi-automatic, or fully automated, first developed in the late part of the 19th century, arc welding became commercially important in shipbuilding during the Second World War. Today it remains an important process for the fabrication of steel structures and vehicles, to supply the electrical energy necessary for arc welding processes, a number of different power supplies can be used. The most common classification is constant current power supplies and constant voltage power supplies, in arc welding, the voltage is directly related to the length of the arc, and the current is related to the amount of heat input. This is important because in manual welding, it can be difficult to hold the electrode perfectly steady, and as a result, the arc length and thus voltage tend to fluctuate. In these processes, arc length is constant, since any fluctuation in the distance between the wire and the base material is quickly rectified by a large change in current. The direction of current used in arc welding also plays an important role in welding, consumable electrode processes such as shielded metal arc welding and gas metal arc welding generally use direct current, but the electrode can be charged either positively or negatively. In welding, the positively charged anode will have a greater concentration and, as a result. If the electrode is charged, it will melt more quickly, increasing weld penetration. Alternatively, a negatively charged electrode results in more shallow welds, non-consumable electrode processes, such as gas tungsten arc welding, can use either type of direct current, as well as alternating current. Alternating current rapidly moves between two, resulting in medium-penetration welds. Duty cycle is an equipment specification which defines the number of minutes, within a 10-minute period. For example, an 80 A welder with a 60% duty cycle must be rested for at least 4 minutes after 6 minutes of continuous welding, failure to observe duty cycle limitations could damage the welder. Commercial- or professional-grade welders typically have a 100% duty cycle, one of the most common types of arc welding is shielded metal arc welding, which is also known as manual metal arc welding or stick welding. An electric current is used to strike an arc between the material and a consumable electrode rod or stick. The electrode core itself acts as filler material, making a separate filler unnecessary, the process is very versatile, requiring little operator training and inexpensive equipment

36.
Oxy-fuel welding and cutting
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Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903, pure oxygen, instead of air, is used to increase the flame temperature to allow localized melting of the workpiece material in a room environment. In recent decades it has been obsolesced in almost all industrial uses due to various arc welding methods offering more consistent mechanical weld properties, gas welding is still used for metal-based artwork and in smaller home based shops, as well as situations where accessing electricity would present difficulties. In oxy-fuel welding, a torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal, the molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded, in oxy-fuel cutting, a torch is used to heat metal to its kindling temperature. A stream of oxygen is then trained on the metal, burning it into an oxide that flows out of the kerf as slag. Torches that do not mix fuel with oxygen are not considered oxy-fuel torches, most metals cannot be melted with a single-tank torch. Consequently, single-tank torches are typically suitable for soldering and brazing, oxy-gas torches are or have been used for, Welding metal, see below. Depositing metal to build up a surface, as in hardfacing, also, oxy-hydrogen flames are used, in stone working for flaming where the stone is heated and a top layer crackles and breaks. A steel circular brush is attached to a grinder and used to remove the first layer leaving behind a bumpy surface similar to hammered bronze. In the glass industry for fire polishing, in jewelry production for water welding using a water torch. in automotive repair, removing a seized bolt. Formerly, to heat lumps of quicklime to obtain a white light called limelight. Formerly, in works, as platinum is fusible only in the oxyhydrogen flame. The apparatus used in gas welding consists basically of an oxygen source and this sort of torch can also be used for soldering and brazing. The cylinders are carried in a special wheeled trolley. There have been examples of oxyhydrogen cutting sets with small gas cylinders worn on the back in a backpack harness, for rescue work. There are also examples of pressurized liquid fuel cutting torches, usually using gasoline and these are used for their increased portability

37.
Sunglasses
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Sunglasses or sun glasses are a form of protective eyewear designed primarily to prevent bright sunlight and high-energy visible light from damaging or discomforting the eyes. They can sometimes function as a visual aid, as variously termed spectacles or glasses exist. In the early 20th century, they were known as sun cheaters. The American Optometric Association recommends sunglasses whenever a person is in the sun. to protect the eyes from ultraviolet radiation and blue light, Sunglasses have long been associated with celebrities and film actors primarily from a desire to mask their identity. Since the 1940s, sunglasses have been popular as a fashion accessory, in prehistoric and historic time, Inuit peoples wore flattened walrus ivory glasses, looking through narrow slits to block harmful reflected rays of the sun. It is said that the Roman emperor Nero liked to watch gladiator fights with emeralds and these, however, appear to have worked rather like mirrors. Sunglasses made from flat panes of smoky quartz, which offered no corrective powers, ancient documents describe the use of such crystal sunglasses by judges in ancient Chinese courts to conceal their facial expressions while questioning witnesses. James Ayscough began experimenting with tinted lenses in spectacles in the mid-18th century and these were not sunglasses as that term is now used, Ayscough believed that blue- or green-tinted glass could correct for specific vision impairments. Protection from the Suns rays was not a concern for him, in the early 1920s, the use of sunglasses started to become more widespread, especially among movie stars. The stereotype persisted long after improvements in quality and the introduction of ultraviolet filters had eliminated this problem. Inexpensive mass-produced sunglasses made from celluloid were first produced by Sam Foster in 1929, Foster found a ready market on the beaches of Atlantic City, New Jersey, where he began selling sunglasses under the name Foster Grant from a Woolworth on the Boardwalk. By 1938, Life magazine wrote of how sunglasses were a new fad for wear on city streets, a favorite affectation of thousands of women all over the U. S. It stated that 20 million sunglasses were sold in the United States in 1937, Polarized sunglasses first became available in 1936, when Edwin H. Land began experimenting with making lenses with his patented Polaroid filter, at present, Xiamen, China, is the worlds largest producer of sunglasses, with its port exporting 120 million pairs each year. Sunglasses can improve comfort and visual clarity by protecting the eye from glare. Various types of disposable sunglasses are dispensed to patients after receiving mydriatic eye drops during eye examinations, the lenses of polarized sunglasses reduce glare reflected at some angles off shiny non-metallic surfaces, such as water. They allow wearers to see into water when only surface glare would otherwise be seen, Sunglasses offer protection against excessive exposure to light, including its visible and invisible components. Sunglasses that meet this requirement are often labeled as UV400 and this is slightly more protection than the widely used standard of the European Union, which requires that 95% of the radiation up to only 380 nm must be reflected or filtered out

38.
Braincase
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In mammals, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull. The skull can be divided into two parts, the neurocranium, which forms a case around the brain, and the facial skeleton. In the human skull, the neurocranium includes the calvaria or skullcap, the lower part of the skull is the facial skeleton, also known as the splanchnocranium. There may variably also be extra sutural bones present, below the neurocranium is a complex of openings and bones, including the foramen magnum which houses the neural spine. The auditory bullae, located in the region, aid in hearing. The size of the neurocranium is variable among mammals, the roof may contain ridges such as the temporal crests. The neurocranium arises from paraxial mesoderm, there is also some contribution of ectomesenchyme. In Chondrichthyes and other cartilaginous vertebrates this portion of the cranium does not ossify, the neurocranium is formed by the endocranium, the lower portions of the cranial vault, and the skull roof. These are not fused in fishes, and a proper neurocranium is only found in land vertebrates, the upper-frontmost part of the cranium also houses the evolutionarily newest part of the human brain, the frontal lobes

39.
Mixed martial arts
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Mixed martial arts is a full-contact combat sport that allows both striking and grappling, both standing and on the ground, using techniques from other combat sports and martial arts. The first documented use of the mixed martial arts was in a review of UFC1 by television critic Howard Rosenberg in 1993. The term gained popularity when newfullcontact. com, then one of the largest websites covering the sport, the question of who actually coined the term is subject to debate. During the early 20th century, various mixed-style contests took place throughout Japan, in 1980 CV Productions, Inc. created the first regulated MMA league in the United States, named Tough Guy Contest, later renamed Battle of the Superfighters. The company sanctioned ten tournaments in Pennsylvania, however, in 1983 the Pennsylvania State Senate passed a bill prohibiting the sport. In 1993, the Gracie family brought vale tudo, developed in Brazil from the 1920s, later, individual fighters employed multiple martial arts into their style. MMA promoters were pressured to adopt additional rules to increase safety, to comply with sport regulations. Following these changes, the sport has increased popularity with a pay-per-view business that rivals boxing. In Ancient Greece there was a sport called pankration, which featured a combination of grappling and striking skills similar to found in modern MMA. Pankration was formed by a combination of the already established wrestling and boxing traditions and, in Olympic terms, All strikes and holds were allowed with the exception of biting and gouging, which were banned. Fighters, also known as pankratists, fought until a fighter submitted, according to E. Norman Gardiner, No branch of athletics was more popular than the pankration. From its origins in Ancient Greece, pankration was later passed on to the Romans, the mid nineteenth century saw the prominence of the new sport savate in the combat sports circle. At that time, French fighters wanted to test out the sport against the traditional styles of its time. However, the English team still won the four other match-ups during the contest, since then other similar contest also occurred by the late 19th to mid-20th century between French Savateurs and other combat styles. The next publicized encounter occurred in the late 1890s when future heavyweight boxing champion Bob Fitzsimmons took on European Greco-Roman Wrestling champion Ernest Roeber. In September 1901, Frank Paddy Slavin, who had been a contender for Sullivans boxing title, knocked out future world wrestling champion Frank Gotch in Dawson City, Canada. The judo-practitioner Ren-nierand who gained fame after defeating George Dubois, would again in another similar contest against Ukrainian wrestler Ivan Poddubny. Another early example of mixed martial arts was Bartitsu, which Edward William Barton-Wright founded in London in 1899, merikan contests were fought under a variety of rules, including points decision, best of three throws or knockdowns, and victory via knockout or submission

40.
Water polo cap
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A Water polo cap is a piece of headgear used in water polo and a number of underwater sports. The caps are used to both the player and their team, and to protect their ears from injury possibly caused by a water polo ball hitting the head. Caps are differentiated by the number printed on them as well as the color, players from the visiting team will wear white caps, whereas the home team players will wear blue caps. The goalkeepers wear quartered red caps, numbered 1, while substitute goalies have caps which are either numbered 1-A in NCAA games, opponents in underwater hockey and underwater rugby wear either one of two colours - white or dark caps while the water referees wear red caps. Underwater football appears to follow this precedent, caps are also used in Aquathlon for identification purposes, one competitor wears either a red or blue coloured cap while the other competitor wears a white or yellow coloured cap

41.
Underwater hockey
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Underwater Hockey is now played worldwide, with the Confédération Mondiale des Activités Subaquatiques, abbreviated CMAS, as the world governing body. The first Underwater Hockey World Championship was held in Canada in 1980 after a start in 1979 brought about by international politics. Two teams of up to ten players compete, with six players in each team in play at any one time. The remaining four players are substituted into play from a substitution area. Before the start of play the puck is placed in the middle of the pool, at the start-of-play signal in-play members of both teams are free to swim anywhere in the play area and try to score by manoeuvring the puck into the opponents goal. Players hold their breath as they dive to the bottom of the pool, play continues until either a goal is scored, when players return to their wall to start a new point, or a break in play is signalled by a referee. Games consist of two halves of ten to fifteen minutes and a short half-time interval of usually three minutes. At half time the two teams switch ends, a typical playing formation is 3-3 of which 3-2-1 is a variation. Other options include 2-3-1, 1-3-2, or 2-2-2, formations are generally very fluid and are constantly evolving with different national teams being proponents of particular tweaks in formations, such as New Zealand with their box formation. If the penalty is minor, referees award an advantage puck, for major penalties, such as a dangerous pass or intentional or repeated fouls, the referees may eject players for a specified period of time or the remainder of the game. A defender committing a serious foul sufficiently close to his own goal may be penalized by the award of a penalty shot, since this is an underwater sport, surface spectators may be unaware of just how physical Underwater Hockey is. It is also important that they are able to well with their team members. Click to find out more about Underwater Hockey by watching a small clip, although Underwater Hockey is a non-contact sport, there is a significant risk of injury. 3-1.5 kg puck resulting in concussions, deep cuts to the head or dental trauma. Personal protective equipment is available to reduce these risks, There is also a risk of pulmonary capillary stress failure in some players. Players wear a mask, snorkel and fins, and carry in one hand a short stick for playing the puck. A full list of equipment is given below, There are usually no restrictions on swimwear, however baggy style trunks or shorts are not recommended as they reduce speed, typical swimwear is swim briefs for male players and one-piece swimsuits for female players. The rules require masks to have two lenses to reduce the risk and extent of injury due to puck impact with a lens. A variety of webbing strap designs are available to replace the head strap with a non-elastic strap that reduces the chances of the player being unmasked

42.
Water polo
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Water polo is a competitive team sport played in the water between two teams. The game consists of four quarters, in which the two attempt to score goals by throwing the ball into their opponents goal. The team with the most goals at the end of the game wins the match, each team made up of six field players and one goalkeeper, with typically six additional players available for substitution throughout the match. Except for the goalkeeper, players participate in offensive and defensive roles. Water polo is played in an all-deep pool seven feet deep. The game is thought to have originated in Scotland in the late 19th century as a sort of water rugby, William Wilson is thought to have developed the game during a similar period. Mens water polo was among the first team sports introduced at the modern Olympic games in 1900, Water polo is now popular in many countries around the world, notably Europe, the United States, Canada and Australia. The present-day game involves teams of seven players, with a polo ball similar in size to a soccer ball. One of the earliest recorded viewings of water polo was conducted at the 4th Open Air Fete of the London Swimming Club, held at the Crystal Palace, another antecedent of the modern game of Water Polo was a game of water ‘hand-ball’ played at Bournemouth on 13 July 1876. This was a game between 12 members of the Premier Rowing Club, with goals being marked by four flags placed in the water near to the midpoint of Bournemouth Pier. The game started at 6,00 pm in the evening and lasted for 15 minutes watched by a large crowd, the rules of water polo were originally developed in the late nineteenth century in Great Britain by William Wilson. Wilson is believed to have been the First Baths Master of the Arlington Baths Club in Glasgow, the first games of aquatic football were played at the Arlington in the late 1800s, with a ball constructed of India rubber. This water rugby came to be called water polo based on the English pronunciation of the Balti word for ball, early play allowed brute strength, wrestling and holding opposing players underwater to recover the ball. Players held underwater for lengthy periods usually surrendered possession, the goalie stood outside the playing area and defended the goal by jumping in on any opponent attempting to score by placing the ball on the deck. The rules of water cover the play, procedure, equipment. These rules are similar throughout the world, although variations to the rules do occur regionally. There are seven players in the water from each team at one time, there are six players that play out and one goalkeeper. Unlike most common sports, there is little positional play

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Formula One
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Formula One is the highest class of single-seat auto racing that is sanctioned by the Fédération Internationale de lAutomobile. The FIA Formula One World Championship has been the form of racing since the inaugural season in 1950. The formula, designated in the name, refers to a set of rules, the F1 season consists of a series of races, known as Grands Prix, held worldwide on purpose-built F1 circuits and public roads. The results of each race are evaluated using a system to determine two annual World Championships, one for drivers, one for constructors. The racing drivers are required to be holders of valid Super Licences, the races are required to be held on tracks graded 1, the highest grade a track can receive by the FIA. Most events are held in locations on purpose-built tracks, but there are several events in city centres throughout the world. Formula One cars are the fastest road racing cars in the world. Formula One cars race at speeds of up to approximately 375 km/h with engines currently limited in performance to a maximum of 15,000 RPM, the cars are capable of lateral acceleration in excess of five g in corners. The performance of the cars is very dependent on electronics – although traction control and other driving aids have been banned since 2008 – and on aerodynamics, suspension, the formula has radically evolved and changed through the history of the sport. F1 had a global television audience of 425 million people during the course of the 2014 season. Grand Prix racing began in 1906 and became the most popular internationally in the second half of the twentieth century. The Formula One Group is the holder of the commercial rights. Its high profile and popularity have created a major merchandising environment, since 2000 the sports spiraling expenditures and the distribution of prize money favoring established top teams have forced complaints from smaller teams and led several teams to bankruptcy. On 23 January 2017 it was confirmed that Liberty Media had completed its $8 billion acquisition of Delta Topco, the Formula One series originated with the European Grand Prix Motor Racing of the 1920s and 1930s. The formula is a set of rules that all cars must meet. Formula One was a new formula agreed upon after World War II during 1946, the first world championship race was held at Silverstone, United Kingdom in 1950. A championship for constructors followed in 1958, national championships existed in South Africa and the UK in the 1960s and 1970s. Non-championship Formula One events were held for years, but due to the increasing cost of competition

44.
Amelia Earhart
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Amelia Mary Earhart was an American aviation pioneer and author. Earhart was the first female aviator to fly solo across the Atlantic Ocean, distinguished Flying Cross for this accomplishment. She set many records, wrote best-selling books about her flying experiences and was instrumental in the formation of The Ninety-Nines. In 1935, Earhart became a faculty member at Purdue University as an advisor to aeronautical engineering. She was also a member of the National Womans Party and a supporter of the Equal Rights Amendment. During an attempt to make a flight of the globe in 1937 in a Purdue-funded Lockheed Model 10 Electra. Fascination with her life, career and disappearance continues to this day, Earhart was the daughter of Samuel Edwin Stanton Earhart and Amelia Amy. Amelia was the child of the marriage, after an infant stillborn in August 1896. She was of part German descent, alfred Otis had not initially favored the marriage and was not satisfied with Edwins progress as a lawyer. According to family custom, Earhart was named after her two grandmothers, Amelia Josephine Harres and Mary Wells Patton, from an early age, Earhart, nicknamed Meeley was the ringleader while her younger sister, Grace Muriel Earhart, nicknamed Pidge, acted the dutiful follower. Both girls continued to answer to their childhood nicknames well into adulthood and their upbringing was unconventional since Amy Earhart did not believe in molding her children into nice little girls. A spirit of adventure seemed to abide in the Earhart children, as a child, Earhart spent long hours playing with sister Pidge, climbing trees, hunting rats with a rifle and belly-slamming her sled downhill. Although this love of the outdoors and rough-and-tumble play was common to many youngsters, the girls kept worms, moths, katydids and a tree toad in a growing collection gathered in their outings. In 1904, with the help of her uncle, she cobbled together a home-made ramp fashioned after a roller coaster she had seen on a trip to St. Louis, Earharts well-documented first flight ended dramatically. She emerged from the wooden box that had served as a sled with a bruised lip, torn dress. She exclaimed, Oh, Pidge, its just like flying, although there had been some missteps in his career up to that point, in 1907 Edwin Earharts job as a claims officer for the Rock Island Railroad led to a transfer to Des Moines, Iowa. The next year, at the age of 10, Earhart saw her first aircraft at the Iowa State Fair in Des Moines and her father tried to interest her and her sister in taking a flight. One look at the rickety flivver was enough for Earhart, who asked if they could go back to the merry-go-round

Cross section of the olfactory bulb of a rat, stained in two different ways at the same time: one stain shows neuron cell bodies, the other shows receptors for the neurotransmitterGABA.

Neurons generate electrical signals that travel along their axons. When a pulse of electricity reaches a junction called a synapse, it causes a neurotransmitter chemical to be released, which binds to receptors on other cells and thereby alters their electrical activity.

The Neo-Assyrian Empire arose in the 10th century BC. Ashurnasirpal II is credited for utilizing sound strategy in his …

Assyria's greatest pre-reform military commander, Ashurnasirpal II

An image of Tiglath Pileser III's troops (not II). In the background can be seen a siege engine.

Assyrian army crosses a river, probably Euphrates. Some soldiers are swimming while others are loading chariots on to a boat. Reign of Ashurnasirapl II, 865–860 BC, from Nimrud, Iraq, currently housed in the British Museum

''The Pancrastinae'': A statue portraying the pancratium, an event showcased at the Roman Colosseum. Even as late as the Early Middle Ages, statues were put up in Rome and other cities to honour remarkable pankratiasts. This statue, now part of the Uffizi collection, is a Roman copy of a lost Greek original, circa 3rd century BC.

A scene of Ancient Greek pankratiasts fighting. Originally found on a Panathenaic amphora, Lamberg Collection.

A classic 4–2 man-up situation. The attacking white team has 4 players positioned on 2 metres, and 2 players positioned on 4 metres. The 5 outfield defending blue players try to block shots and prevent a goal being scored for the 20 seconds of man-down play. In the top left corner, the shot clock can be seen, showing 28 seconds remaining in the white attack.